A small percent of whites have an allele that is associated with hemochromatosis--a hereditary disorder in which iron salts are deposited in the tissues, leading to liver damage, diabetes mellitus, and bronze discoloration of the skin. This polymorphism is completely absent in West African blacks. This is the kind of difference race deniers tell us doesn't happen.
In this new study, researchers estimated the European ancestry of African Americans using the frequency of this hemochromatosis allele.
They found that, indeed, the frequency of the allele is 0.00000 in people from the Gambia, Nigeria, Senegal, and Sierra Leone. The frequency in white Americans was 0.060-0.067. For all black Americans it was 0.012.
The average white ancestry for black Americans was 0.180 for the whole sample, but it differed by city:
Proportion white ancestry
Rochester, NY 0.132
Birmingham, AL 0.146
Upper Savannah Region, SC 0.157
Portland, OR 0.161
San Diego, CA 0.175
Hartford, CT 0.178
District of Columbia 0.196
Oakland, CA 0.238
Irvine, CA 0.243
The proportion white of blacks living in Irvine is 1.8 times higher than for those living in Rochester, NY, so the variation is noteworthy. I don't see a clear regional pattern here.
The authors report that their findings are consistent with studies using other methods. They also found both paternal and maternal contributions of white American ancestry in black Americans.
